This invention relates to the production of waxes useful in a number of applications requiring waxes that meet exacting standards such as coating materials, adhesives, candles, cosmetics, food and drug applications. More particularly, this invention relates to the production of waxes produced by the reaction of carbon monoxide and hydrogen, the Fischer-Tropsch hydrocarbon synthesis process. Still more particularly, this invention relates to a process whereby at least a portion of raw Fischer-Tropsch wax is subjected to a mild isomerization and blended into untreated Fischer-Tropsch wax to achieve desirable properties.
The catalytic production of higher hydrocarbon materials from synthesis gas, i.e. carbon monoxide and hydrogen, commonly known as the Fischer-Tropsch process, has been known for many years. Such processes rely on specialized catalysts.
The original catalysts for Fischer-Tropsch synthesis were typically Group VIII metals, particularly cobalt and iron, which have been adapted for the process throughout the years to produce higher hydrocarbons. As the technology developed, these catalysts became more refined and were augmented by other metals that function to promote their activity as catalysts. Such promoter metals include the Group VIII metals, such as platinum, palladium, ruthenium, and iridium, other transition metals such as rhenium and hafnium as well as alkali metals. The choice of a particular metal or alloy for fabricating a catalyst to be utilized in Fischer-Tropsch synthesis will depend in large measure on the desired product or products.
The products from hydrocarbon synthesis are useful in a variety of applications. The waxy product of hydrocarbon synthesis, particularly the product from a cobalt based catalyst process contains a high proportion of normal paraffins. It is generally known to catalytically convert the paraffin wax obtained from the Fischer-Tropsch process to lower boiling paraffinic hydrocarbons falling within the gasoline and middle distillate boiling ranges, primarily by hydrogen treatments, e.g. hydrotreating, hydroisomerization and hydrocracking. However, new markets continue to expand in demand for petroleum and synthetic waxes. The varied and growing uses for the waxes, e.g. food containers, waxed paper, coating materials, electrical insulators, candles, crayons, markers, cosmetics, etc. have lifted this material from the by-product class to the product class in many applications.
Stringent requirements are set by regulatory authorities such as the FDA in the United States and the SCF in the European Union, which a wax should meet, particularly if the wax is to be used in food and drug applications. Further, it is a demanding task for the crude oil refiner to meet those requirements. Petroleum waxes derived from crude oil often have dark color, poor odor and numerous impurities requiring significant further refining, particularly when wax is to be used in food and drug applications which require highly refined wax in order to satisfy regulatory authorities. The presence of sulfur, nitrogen and aromatic species, which induce a yellowish or brownish color, are undesirable and may present considerable health risks. Intensive wax refining techniques are required to improve thermal and light properties, ultra-violet stability, color, storage stability and oxidation resistance of the end products. Typically, such waxes are subjected to wax decolorization processes commonly denoted as wax finishing. Such methods are part of a time consuming and costly process and have a detrimental effect on opacity which is desirable in a number of applications where superior thermal and light properties, ultra-violet stability, color and storage stability are desired. These applications include, but are not limited to coating materials, crayons, markers, cosmetics, candles, electrical insulators and the like as well as food and drug applications.
Waxes prepared by the hydrogenation of carbon monoxide via the Fischer-Tropsch process have many desirable properties. They have high paraffin contents, an opaque white color, and are essentially free of any sulfur, nitrogen and aromatic impurities found in petroleum waxes. However, untreated Fischer-Tropsch waxes may contain a small quantity of olefins and oxygenates (e.g. long chain primary alcohols, acids and esters) which can cause corrosion in certain environments. In addition Fischer-Tropsch waxes are harder than conventional petroleum waxes. The hardness of waxes and wax blends as measured by needle penetration can vary considerably. Wax hardness is generally measured by the needle penetration test ASTM D 1321. In general, the hardness of Fischer Tropsch waxes is an advantage since there exists a shortage of high-grade hard paraffin waxes. However, such hardness could limit the usefulness of untreated Fischer-Tropsch waxes in certain applications. Fischer-Tropsch waxes typically undergo severe hydroprocessing to obtain high purity. Virgin Fischer-Tropsch waxes subjected to these prior art processes tend to lose their opaque white property and may become so soft in the process as to render them commercially undesirable requiring costly additives to effect opacity and adjust hardness. It is therefore desirable to provide a hydroprocessing method by which the hardness of these waxes could be adjusted to within selected ranges while maintaining the desirable opaque white property of the untreated raw Fischer-Tropsch wax, thus reducing or eliminating the need for costly additives and further treatment.
In one embodiment, the invention is directed toward a blending process, which retains the desirable properties of a Fischer-Tropsch wax, e.g. the opacity, while adjusting the hardness of the wax to within to a desired range. In another embodiment the invention utilizes a synergistic effect between hard virgin Fischer-Tropsch wax and softer mildly isomerized Fischer-Tropsch wax in a blending process which allows the artisan to adjust the hardness of a wax product to a desired range. The process involves passing a Fischer-Tropsch wax over a hydroisomerization catalyst under predetermined conditions including relatively mild temperatures such that chemical conversions (e.g., hydrogenation and mild isomerization) take place while less than 10% boiling point conversion (hydrocracking) occurs, thus preserving overall isomerized wax yield. At least a portion of the resulting isomerized wax is then blended with untreated hard virgin Fischer-Tropsch wax to adjust the harness thereof.
In another embodiment of the present invention, synthesis gas (hydrogen and carbon monoxide in an appropriate ratio) is fed into a Fischer-Tropsch reactor, preferably a slurry reactor, and contacted therein with an appropriate Fischer-Tropsch catalyst. A hard virgin Fischer-Tropsch wax product is recovered from the reactor. At least a portion of this hard virgin Fischer-Tropsch wax is then introduced into a hydroisomerization process unit along with hydrogen and contacted therein with a hydroisomerization catalyst under mild hydroisomerization conditions. The resulting softer isomerized wax is then blended with untreated hard, virgin Fischer-Tropsch wax in such an amount that a desired hardness of the blended wax is achieved. In a more preferred embodiment, the softer isomerized wax is blended with untreated hard virgin Fischer-Tropsch wax in such an amount that a desired hardness of the blended wax is achieved while maintaining an opaque white color comparable to that of the untreated hard virgin Fischer-Tropsch wax.